1. Field of the Invention
This invention is in the field of manufacturing semiconductor laser diodes with buried hetero-structures wherein multiple layers of heterogenous composition are contacted with a semiconductor melt containing a dopant under conditions such that there is a solution equilibrium between the semiconductor material and at least some of the layers so that neither significant epitaxial deposition nor erosion of semiconductor material occurs from these layers but diffusion of the dopant from the melt into the adjacent zones occurs.
2. Description of the Prior Art
Semiconductor laser diodes with buried hetero-structure are known as BH lasers (buried hetero-laser). Such lasers include a substrate body and a vertical series of semiconductor layers forming the double hetero-layer structure. Between them, the layers provide a strip shaped laser zone. Contact electrodes are applied for supplying electrical current to the laser diode.
The manufacture of a BH laser with one or more barrier layers in adjoining regions usually involves two epitaxial deposition processes. In the first process, the double hetero-layer structure is generated across the entire surface of the substrate. The laser strip consisting of a narrow strip is then etched out of this structure and a contact electrode is applied thereto. In the second epitaxial process, the lateral regions which extend next to the strip of the double hetero-structure and above the lateral parts of the substrate are filled with semiconductor material. At least two semiconductor layers having opposite doping (n-p or p-n) are thereby epitaxially deposited so that an inhibiting layer sequence npn or pnp is present. The material of the substrate itself may also be included in the layer sequence of hetero-layer structures. Such a BH laser and a manufacturing method employing such epitaxial depositions including pn junctions in the lateral regions is disclosed in U.S. Pat. No. 4,426,700.
A laser diode having a different structure, namely, an RIDS laser, is known from Appl. Phys. Letters, Vol. 43 (1983), pages 809 to 811. In contrast to the BH structure, this RIDS laser has layers of diffusion-doped areas. This area-wide diffusion in one layer is based on a correspondingly area-wide diffusion of the particular dopant from a layer lying above which exists as a monolithic layer. The layer of the diffusion source remains as a permanent component of the finished laser diode.
One of the problems in the RIDS laser and in the manufacturing thereof, is to dope a central strip entirely through the strip by means of diffusion from the thickness direction. In order to achieve this, the substrate body of the known diode has been provided with a strip, even before application of any epitaxial layers whatever, whose geometric dimensions correspond to a web present in a BH laser. The function of this web is only to achieve a different layer thickness of at least a first layer deposited on the substrate member over the deposition area. Layers inhibiting electrical current flux laterally relative to the laser-active zone of the RIDS laser are epitaxially generated from the material already doped.
It is difficult, however, to grow the material of the second epitaxial process without fault at the lateral surfaces of the heterogenous layer sequence to such an extent that no leakage current paths will occur between the double hetero-layer structure and the inhibiting pn junction structure of the adjoining regions.